Remove security release check from PassingBuild

This essentially removes the concept of a "security" auto-deploy build, since auto-deploys are now always handled on the Security mirror.

Because Security mirrors also run full test suites reliably, we no longer want to naively use to the latest commit, but instead require a passing commit that's also mirrored to Build.

Closes gitlab-com/gl-infra/delivery#1133 (closed)

See also gitlab-com/chatops!165 (merged)